program sq;
var r1,r2,r3:real;

function square(r1,r2,r3:real):real;
begin
square:=pi*((r1*r1)/2+(r2*r2)-(r3*r3)*2);
end;

begin
write('radius 1 ');
readln(r1);
write('radius 2 ');
readln(r2);
write('radius 3 ');
read(r3);

write('square is ',square(r1,r2,r3):1:2);
end.